In general, a wireless communication system with multiple transmit/receive antennas has a larger channel capacity than a single-antenna wireless communication system.
Double space time transmit diversity (DSTTD) implements two Alamouti STTDs. The Alamouti STTD-based communication system achieves a transmit diversity gain, especially a spatial multiplexing gain, due to its parallel structure. Meanwhile, the multi-antenna wireless communication system can operate using orthogonal frequency division multiplexing (OFDM) to minimize frequency selective fading.
To obtain optimal performance, a DSTTD-OFDM communication system should use an ML receiver. However, real implementation of the DSTTD-OFDM communication system is hard because the use of an ML receiver requires exponential functional complexity in the number of transmit antennas and the modulation order used.